With the development in the early 1970's of frequency-stabilized, single-frequency dye lasers, and particularly with the introduction of commercially-available versions capable of a 30 GHz continuous scan range, this type of laser became the standard tool for high resolution spectroscopy. Once the frequency stability of this source was brought under electronic control, it became possible to develop its other aspects. In particular the laser frequency-scanning elements have been put under computer control to allow very long scans (1000 GHz), and wavemeters, or means of precisely monitoring the laser output frequency, have been developed.
Use of such wavemeters is one approach to solve the "search mode" problem. The electronically-stabilized laser's linewidth is typically 1 MHz or less. Even after setting the output wavelength with a typical low-resolution laboratory spectrometer to within 1'.ANG. (.about.100 GHz), there are still 10.sup.5 resolution elements to search over to find a desired 1 MHz feature.
Once the usefulness in laser spectroscopy of a wavemeter of 1.times.10.sup.-6 or better precision was demonstrated, others suggested additional alternative designs and improvements for such instruments. Today there are several laser-wavemeter instruments commercially available.
But existing wavemeters have definite drawbacks. They are stand-alone devices, and while under the control of a computer, are not integrated with the scannable dye laser. They are large, complicated, and expensive and have stringent optical alignment requirements to be accurate.